INDUSTRIAL A N D ENGINEERING CHEMISTRY
564 Table
1.
Anrlysis of Knowns
Sample Amount of 0.001 A', Iodine No. Sample Solution, Net
M1.
Ml. 25 25 25 25 25 25 10 10 6 Speoifio gravity of samples
Carbon Disulfide Present Found Difference P.p.m. P.p.m. P.p.m.
1.1 0.58 1.0 2.2 1.16 2.0 xn 3.2 1.68 5.3 5.0 2.78 10.0 10.1 5.29 12.89 25.0 24.6 49.0 50.0 10.27 100.0 98.4 20.63 196.0 200.0 20.65 at 20°/4" C. 1.6937
-
fO. 1 +0.2 +0.2 +0.3 +o. 1 -0.4 -1.0 -1.6
-4.0
tion slightly acid by the addition of dilute acetic acid from a buret until 3 or 4 dro s in excess are indicated. Immediately add 50 ml. of ethyl alcotol (3A specially denatured) connect the flask to the titration apparatus, and titrate to a dead-stop end point with 0.001 N iodine solution. Similarly treat a blank containing all the reagents and omitting the sample. At the start of the titration the galvanometer will show no reading. As the end point is a proached the galvanometer will show a temporsry deflection of aiout 3 scale divisions aa each drop of iodine reagent is added. At the true end oint one drop of reagent cauws a permanent galvanometer deflection of 3 to 5 scale divisions. However, greater speed in the titrat@ may be obtained without loss in accuracy by choosing a point at 10 or 15 on the galvanometer scale as the final end point and titrating to this same point with the blank and all the samples. CALCULATION. 1 ml. of 0.001 N iodine = 76 micrograms of carbon disulfide. EXPERIMENTAL RESULTS
The first series of experiments was made to find the time required to complete the reaction of the carbon disulfide with the alcoholic potassium hydroxide, and to determine the stability of the xanthate formed. Knowns of from 1 to 200 p.p.m. of carbon disulfide were used for this experiment. Figure 1shows that any Length of time from 30 minutes to 2 hours may be allowed for this
Vol. 17, No. 9
reaction. However, the 30-minute point was chosen for a routine procedure to speed up the analysis. A second series of experiments was carried out to determine the precision and accuracy of the method when applied to carbon tetrachloride containing various amounts of carbon disulfide (Table I). The samples were pre ared by carefully weighing known quantities of carbon disulfife in a weighed 100-ml. glass-sto pered volumetric flask containing about 25 ml. of carbon disulficfe-free carbon tetrachloride. The mixture was then diluted to the mark at 20" C. Ali uots of this first 100-ml. mixture were measured from a jacketel buret at 20" C. and further diluted with carbon tetrachloride to obtain the desired knowns. SUMMARY
The method described in this paper was found to be very practical and rapid, giving a relatively high degree of precision and accuracy. It was especially useful in routine work where a large number of samples, with approximately the same amount of carbon disulfide impurity, had to be analyzed in a short time. ACKNOWLEDGMENT
The authors are indebted to F. J. Hopkinson of the Induvtrial Laboratory for many helpful suggestions and for the equipment used in this work. LITERATURE CITED
(1) Dept. Sci. Ind. Research (Brit.), Leaflet 6 (1939). (2) Huff, J. Am. Chem. SOC.,48,81-7(1926). (3) Mstusaak, M.P.,IND.ENG.CHEM.,ANAL.ED., 4,98(1932). (4) Moskowitz, Siegel, and Burke, N . Y. State I d . Bull., 19, 8:i (1940). (5) Serfass, E. J., IND.ENG.CHEM.,ANAL.ED.,12, 536-9 (1940). (6) Viles, J . I d . Hug. TozieOl., 22, 188 (1940). (7) Wernimont, G.,and Hopkinson, F. J., IND. ENQ. CHEM.,ANAL. ED., 12, 308-10 (1940). (8)Ibid., 15, 273 (1943).
Analysis of Cyclopropane-Propylene Mixtures by Selective Hydrogenation E. S. CORNER'
AND
R. N. PEASE, Frick
Chemical Laboratory, Princeton University, Princeton,
N. 1.
A new method, presented for the analyaia of cyclopropanepropylene mixtures b y selective hydrogenation, consiats in passing the mixture with hydrogen over a nickel-kieselguhr catalyst partially poisoned with mercury to hydrogenate the olefin, then over a nonpoisoned catalyst to hydrogenate the cyclopropane. Accu-
racies of *0.5 numerical % are obtained. The presence of inert components auch as gaaeous paraffina does not interfere with the analysis and hence a real advantage is realized over other methods deacribad in the literature. Small samplea ("1 cc. N.T.P.) may be analyzed with good accuracy.
A
tion occurred only at temperatures above 80" C. while propylene was easily hydrogenated a t room temperatures. Accordingly, hydrogenation studies were undertaken in an attempt to apply this reported differential effect to a scheme of analysis. Preliminary experiments were carried out using a nickel catalyst supported on kieselguhr. Results showed that this catalyst after reduction in hydrogen completely reduced cyclopropane to propane in a few passes over the catalyst a t temperatures as low as 0" C. Consequently, a reduction of the activity by partial poisoning was attempted. It was found that the introduction of a few drops of mercury sufficiently deactivated the catalyst so that reduction of propylene waa complete after a few pesses while cyclopropane was unchanged a t temperatures up to 200" C. The poisoning technique ia described below. A nonpoisoned catalyst was used for the hydrogenation of cyclopropane, Presumably the differences in activity of the Willstatter and Bruce catalyst and the one employed by the authors are attribut-
SEARCH of the literature reveals no method for the direct determination of cyclopropane. Several methods for the analysis of binary mixtures of propylene and cyclopropane have been proposed, the most widely used of which is based upon absorption of the propylene in a 3% aqueous potassium permanganate solution (I, t , 4 ) . Cyclopropane is found by difference after correcting for solubility effects. However, in the presence of saturated hydrocarbons or other inert gasas, no analysis is possible. A new method, based upon selective hydrogenation, provides a direct analysis for cyclopropane. In addition, mall gas volumes (-1 cc. a t normal temperature and p m u r e ) may be analyzed. Willstlitter and Bruce (b) studied the hydrogenation of cyclopropane over a nickel catalyst and found that appreciable reacI Praent ddreu, Elso Laborstorica, Standard Oil DePdopmsnt Co.. Elirabrtb, N. J.
ANALYTICAL EDITION
September, 1945
Figure 1.
Diagram of Apparatus
able to differences in composition and method of preparation. The catalyst used in the authors' experiments is described by Trenner, blorikawa, and Taylor (3)aa follows: "The nickel catalyst was a very active nickel-kieselguhr preparation, made by precipitation of the carbonate on kieselguhr, ignition, and reduction in hydrogen a t progreesively increasing temperature to 450'. I t contained 15% nickel." Willstiitter and Bruce (5) describe their catalyst as a mixture of equal parts of nickel oxide and pumice, reduced to the metal a t 280" C. A second difficulty encountered was adsorption on the cat* lyst surface. Saturation with hydrogen or with a hydrogenhydrocarbon mixture before analysis proved unsatisfactory because of unequal sdsorption of the constituents of the mixture. These effects were eliminated by evacuating the catalyst chambers with a Toepler pump after each hydrogenation and returning the recovered gasea to the sample. As a further precaution, small volumcs of catalyst were employed. The expected volumes were recovered within experimental error in all cases. Since the usual stopcock greases absorb hydrocarbone readily, it was necessary to employ a lubricant made up of glycerol, dextrin, and mannitol, in which hydrocarbons are nearly insoluble.
at approximately 300". Mercu waa driven off the poisoned catalyst, after w h i x the activity returned to normal aa measured by its ability to reduce cyclopropane readily. The catal st was again poiwned by the technique describedl ANALYTICALPROCEDURE. Before analysis the catal st bulbs (maintained a t 150") were evacuateiwith the Toepler pump with stopcock 3 closed; three pumping8 of each catal st were sufficient. With the Tcepler pum filyd with mercury and stopcock 1 closed, t%e hydrogen pressure was adjusted a t 400 to 500 mm. and the manometer read with the mercury levels a t marks b and c. The hydrocarbon sample was then introduced and the manometer read with the mercury levele at marks b md c aa before. To determine the ole& content, the mixture was passed several times over the poisoned catalyst and the pressure m r d e d after evacuating the catalyst. To check completeness of hydrogenation, the proceaa was repeated. The cyclopropane was then determined over the active catalyst. Saturates, if present, were obtained by ditrerence. The ca fflary tubing must be swept out during the ana&& to ensure contact of all the sample with the catalysts. For small samples, pressum were read with the mercury level adjusted to mark a. Before the mixture was passed over the catalysts, the volume was exDanded bv lowerinn B and reductions were c&ied out-at Iow K O noticeable difference was detecte!;%%tes of hydrogenation a t these reduced ressures. By t h rocedure very small sam lea (-1 cc. N.T.!.) could be analyze$. A buret may ge substituted for bulbs CI and CSfor analyses at constant remure. For m a l l samples it would be neceemry to attach a buyb below a microburet for expansion to facilitate hydrogenation.
-
The details of procedure outlined above apply to the highly active catalyrrt employed. Although the authors have no data on the behavior of lesa active catalysts, with appropriate modification in operating temperature and the like, such differential hydrogenation based on partial poisoning with mercury should be s u c ~ f with d any reasonably active supported catalyst.
E
1.
Analysis of Cyclopropane-Propylene Mixtures (Approximate Hrsample ratio 2 to 1) volumeof Composition of Synth'etic Found by Analysia Table
Sample
+
cc.
100 100 4
100 100
100 4 100 4
APPARATUS AND PROCEDURE
A diagram of the apparatus is shown in Figure 1. Bulbs A1 and A1 each contained 2 or 3 cc. of catalyFt (actually one bulb was placed behind the other). An electrically heated furnace with rheostat control was placed around these bulbs. C1, used for the analysis of small samples, had a capacity of approximately 4 cc., while CI had a volume of 100 cc. These were enclosed in a water jacket. B, which served for pawing the gaseous mixture over the catalysts, was also used as the Toepler pump for evacuating the catalyst bulbs. The manometer, M , completed the apparatus. Capillary tubing throughout minimized the dead space. REDKCTION OF CATALYSTSAND POISONING TECHNIQUE. The catalysts were reduced in a slow $ream of hydrogen, startin. at 250' and slowly increasing to 400 . Tank hydrogen waa pursed by passing first over platinized asbestos and then through a liquid air trap to remove water. After reduction was complete, the temperature was reduced to 150°, the hydroeenation temperature, and one of the cataI sts was partially poisoned. A few drops of mercury from bulg 5 were introduced into the capillar between stopcocks 1 and 2 and then pushed over into the c a t 9 st chamber with hydrogen by lifting bulb D after filling B wit{ hydrogen. The catalyst then ssessed the desired activity. Fifteen or twenty analyses could made before regeneration of the catalysts became necessary. This was carried out by again passing hydrogen over the catalysts
565
100
100a
8
H9
Cyclopropane
Propylene
Cyclopropane
21.6 24.0 33.6 40.0 48.5 73.2 73.8 80.2
78.4 75.4 66.4
27.3
26.1 42.3
100.0 100.0
100. 30.1 Balance of #ample n-butane.
Propylene
Vol. %
Vol. %
60.0
51.5 26.8 26.2 19.8
...
...
21.4
78.6
33.4
66.8 59.7 51.8 27.2 25.9 20.0
24.2
40.0 48.1
72.7 74.3 80.4 89.5 100.2 27.0 3o.a
76.0
... ...
26.2 42.0
RESULTS
Various mixtures of known composition have been analyzed and the resulte are tabulated in Table I. On a numerical percentage basis, accuracies of *0.5% are obtained. An examination of the data reveals little or no difference in precision for the large or small samples-perhaps because of the few data presented. Errors arising from such factors as adjusting mercury levels would be magnified when analyzing small samples. However, it was found that reproducibility in adjusting these levels for one small sample waa within 0.5%. The importance of using a stopcock lubricant in which hydrocarbons are nearly insoluble cannot be overemphasized. Van der Waals corrections for perfect gas deviations were within experimental error and hence no correctiona have been applied.
566
INDUSTRIAL AND ENGINEERING CHEMISTRY
An apparatus similar to the one described, but using only one catalyst, may be employed for determining the olefin content in gaseous mixtures containing only olefins and paraffins. The method possesses definite advantages, since adsorption effects are minimized and very small samples may be handled. CONCLUSIONS
A method developed for the analysis of cyclopropanc-propylene mixtures by selective catalytic hydrogenation with accuracies of *0.5% provides for the direct determination of cyclopropane, and hence the presence of saturated hydrocarbons does not interfere. No data are available gs to possible interference by substituted acetylenes. Other methods described in the literature do not analyze for cyclopropane directly, Propylene is determined
Vol. 17, No. 9
by absorption in a suitable reagent and cyclopropane obtained by difference. The time required for analysis probably represents a saving-for example, from 1to 2 hours are required for the analysis of binary mixtures when using the dilute potassium permanganate procedure (1) while from 15 to 30 minutes are required with this method. An additional advantage is that small samples (-1 cc. N.T.P.) may be handled with good accuracy. LITERATURE CITED
(1) Chambers and Kistiakowsky, J . Am. Chem. SOC.,56,399 (1934). (2) Roginski and Rathmann, Ibid., 55,2800 (1933). (3) Trenner, Morikawa, and Taylor, Ibid., 59,1103 (1937.). (4) Wagner, Ber., 21, 1236 (1888). (5) Willstiitter and Bruce, Ibid., 40,4456 (1907).
Ternary Mixtures of Three Isomeric Hexanes Quantitative M e t h o d OF Analysis VERLE A. MILLER,
Rerearch Laboratories Division, General Motor, Corporation, Detroit, Mich.
Solution temperature mersurements were made using all the isomeric hexrner with both nitrobenzene and diethyl phthalate. Dab rre given which mrke it possible for a hexane ternary mixture compored of 2,s-dimethylbutane, P,3-dimethylbutane, and 2-methylpentane to b e analyzed with an accuracy of 0.5% in approximately one hour.
I
tanes based on their solution temperature in nitrobenzene and diethyl phthalate. This paper covera the extension of this method of analysis to the above-mentioned hexane ternary mixture, This work makes it possible to analyze a ternary mixture composed of 2,2-dimethylbutane, 2,3-dimethylbutane, and 2-methylpentane with an accuracy of 0.5% in approximately one hour.
N CONNECTION with research at the General Motors Research Laboratory it wgs necessary to analyze hexane mixIn the previous paper (6),ths author stated that no mention had been found in the literature of any attempt to use critical tures that contained much smaller quantities of the doublysolution temperature measurements for the quantitative deterbranched than of the singly-branched hexanes. The automatic stills available a t this laboratory are able to separate the isomeric hexanes (6) and, when the dis2,3-DIMETHYLBUTANE tillation curve is supplemented with a refractive index curve, a good analysis of a hexane mixture can be obtained as long aa there is a sufficient quantity of 21.00 25.00 each isomer in the mixture t o obtain a flat portion in both the refractive index and boiling point curves. Table I shows that aa the boiling point of the hexanes increases the refractive index alternates up and down. I n the distillation of the mixtures under investigation there waa not enough 24 2,3-dimethylbutane present to give a flat on the refractive index cuwe. I n the 00 distillation break between 2,2- and 2,343methylbutane the refractive index would rise but before it reached the value for pure 2J-dimethylbutane it would turn downward again, showing that some 2methylpentane was in the distillate. This particular part of the distillate waa a ternary mixture composed of 2,2and 2,Mimethylbutane with %methyl2pentane, the composition of which could not be determined accurately. Figure 1. Bath Temperature from Refractive Index A previous paper (6) described a Diethyl phthalate point dab method for quantitative analysis of ------Nibobenrma point dab - - - - - - - - - Refractive index dab ternary mixtures of three isomeric hep-
